The present invention relates to a metallic hollow structural component with a metallic insert, especially to a turbine blade with a cooling insert.
For example, in the gas turbine propulsion unit construction, it is generally known to cool turbine guide or rotor blades exposed to comparatively high hot gas temperatures by means of cooling air taken off from the propulsion unit compressor at a suitable place and to provide for the respective blade cooling concept a cooling insert installed into the blade interior (see DE-14 76 790). The installation of several cooling inserts into correspondingly geometrically coordinated blade interior spaces is also known (see DE-OS 23 20 581).
In such or similar cases, at least a part of the corresponding blade cooling system is made available by webs, knubs, folds or the like projecting in a material sense from the blade hollow space interior wall and/or the cooling insert outer wall; inter alia a control of the cooling air flowing from the insert into the channel configuration which justifies the needs of the different hot gas temperature influences can be achieved therewith; inter alia; locally uniform or non-uniform cooling air dwell periods or velocities, as required, can therefore be made available.
In the aforementioned or similar known cases, it is a basic prerequisite for an optimum cooling function which is as low in consumption as possible, that the cooling insert or inserts abut during operation "flush", i.e., without play at the geometrically matched inner counter-surface or surfaces of the blade body. However, this basic prerequisite could not be fulfilled heretofore for assembly and manufacturing reasons; notwithstanding aimed-at, very accurate manufacturing techniques, considerable manufacturing tolerances result with the cooling insert as also, for example, with the cast blade core which can be met either not at all or only with relatively high expenditures in afterfinishing operations.
For purposes of assembly of the insert, corresponding installation difficulties additionally result also as consequence of frequently required profile-geometric distortions. In other words, the installation of the insert requires therefore a relatively great component play if the highly complicated afterfinishing expenditures are to be dispensed with, which, however, becomes effective disadvantageously on the operational cooling function because no "flush", respectively, play-free component abutment exists between blade core and insert.
An additional problem results in that the insert must be connected with the blade body in a suitable form, i.e., must be connected practically non-detachably fixedly; this takes place most recently, for example, by brazing processes in a vacuum integrated into the manufacturing process, in which individual blade groups provided with the inserts are subjected to the locally required brazing.
As a result of the component play requirements between the blade body, on the one hand, and the insert, on the other, as mentioned hereinabove within the scope of the prior art blade concepts and manufacturing technologies, it has been practically impossible heretofore to braze the insert with the blade body in a sufficiently accurate position satisfying the operating requirements or possibly weld the same together.
Added to the aforementioned problems is the fact that notwithstanding a practically non-detachable fastening of the insert at the blade body , expansion differences occurring as a condition of operation must be controllable in order to be able to keep within limits undesired component deformations, especially of the insert, as well as structural impairments of the respective cooling system. Thermally conditioned expansion differences have thereby their origin, inter alia, in the differing temperature exposures of the blade body and of the insert.
The present invention is therefore concerned with the task to achieve with a hollow structural component having at least one insert of the type described above, especially with a turbine blade having a cooling insert, an operationally optimal play-free component pairing and fastening favorable from an assembly and manufacturing point of view notwithstanding mutual manufacturing tolerances.
The underlying problems are solved according to the present invention in that the insert is made of a memory material and abuts without play at the inner geometry when exceeding a predetermined temperature threshold value.
On the basis of the specific properties of memory materials which will be described more fully hereinafter, the respective insert can be manufactured so small that it can be inserted without any problems into the corresponding geometrically coordinated inner recess or aperture of the hollow component, respectively, of the blade core, even with unfavorable tolerance pairings. During the metallurgical fastening process, for example, during brazing in a vacuum, the insert expands relatively rapidly when exceeding a predetermined temperature threshold value--i.e., at a threshold temperature lying far below the maximum brazing temperature of about 1350.degree. C.--to such an extent that it abuts without play at the predetermined actual core shape, respectively, inner geometry of the hollow component.
High manufacturing tolerances can thus be permitted in favor of a cost-reduced manufacture, for example, for a turbine blade, respectively, the blade hollow profile body as also for the cooling insert. Notwithstanding such permissive high manufacturing tolerances, the aimed-at freedom of play, an optimum control of the cooling air and a high cooling effect are achieved, for example, with a turbine blade.
The term "memory alloys", respectively, of the "memory effect" stems from the prior discovery that a certain alloy can change between two structural phases in the solid condition when exceeding or falling below a characteristic temperature value. This "memory effect" occurs particularly pronouncedly within the scope of a nickel-titanium alloy, the use of which forms part of the present invention.
The concept of the "memory effect" therefore rests on the experimentally gained impression that the respective alloy component "remembers" its prior shape, which resulted in the coining of terms such as "shape memory effect".
Within the scope of the present invention, on the one hand, one may therefore start with the fact that the respective "memory-insert" maintains a shape mechanically imposed thereon at low temperature up to a so-called "threshold value". Only when the exposure temperature exceeds this "threshold value", the memory insert then remembers its original shape condition, i.e., returns into its original shape. In the course of this re-deformation, the "memory insert" is capable to abut itself without play at the actual core shape of the hollow component, respectively, at the inner contour of the blade hollow profile. This aforementioned "memory effect" is also referred to as so-called "one-way effect". The return-expansion of the "memory insert" which takes place when falling below the temperature threshold value, would have no disadvantage as regards the cooling effectiveness because the temperature threshold value would have to be placed in such a low temperature range (for example, 100.degree.-150.degree. C.), in which a blade cooling would not be necessary anyhow.
The present invention can also be realized without difficulty within the scope of a so-called "two-way memory-effect"; in this case the component is subjected in the martensitic condition a to a relatively strong bending deformation b (with irreversible component) as well as subsequently heated so that a desired high temperature shape c will establish itself in the austenitic phase. If the component is thereafter cooled, then a low temperature shape d will form. When carrying out the temperature cycles, the component therefore "remembers" the high temperature shape c as also the low temperature shape d. The high temperature shape c would therefore be the optimum shape in the instant case in which the insert abuts absolutely play-free at the corresponding inner component geometry. An important advantage of this "two-way effect" is that during component cooling (shape d), only a comparatively slight shape deviation (respectively, expansion change) results between shape c and d, in which freedom of play of the insert (wedging seat) continues to be still possible in a most far-reaching manner, i.e., "freedom of play" and therewith an optimum turbine blade cooling is assured over a comparatively large turbine operating--and hot gas temperature range.